Metamaterials@Southampton
What If We Could Program a Material?
What if a material could do the opposite of what you expect? Most materials follow behaviours that quickly become intuitive. Stretch something and it usually becomes thinner in the directions perpendicular to the applied pull. Compress it and it shortens. But carefully designed materials can break these expectations. A structure can become wider when stretched, twist when compressed, change shape when exposed to a magnetic field, or guide vibrations away from selected regions. Under the right conditions, some (meta-)materials can even exhibit effective negative stiffness or behave as if they possess negative mass, producing responses that seem to defy our everyday intuition about how matter should move and deform.
None of this requires an exotic new chemical substance. The material itself may still be an ordinary polymer, steel, aluminium or composite. What changes is its internal architecture. By designing that architecture, engineers can begin to programme mechanical behaviour. These are mechanical metamaterials.
Imagine replacing a solid block of steel or aluminium with a repeating network of tiny beams: a lattice. Its empty spaces reduce weight, but geometry does much more. Some arrangements carry forces mainly by stretching the beams; others encourage bending, rotation or buckling. Engineers can vary the pattern, beam thickness, angles and connections, predict the response using mechanics and computer simulations, and then manufacture the design using techniques such as 3D printing. The same base material can therefore behave like a stiff support, a flexible spring or an impact absorber. Geometry becomes a set of instructions written into the material.
The figure captures this idea in a historical context. For centuries, engineers have improved structural efficiency by arranging material more intelligently, progressing from massive stone structures to timber frames and highly efficient modern structures. Metamaterials take this idea down to the material scale (i.e. lower length scales, such as micro and nano). Instead of designing only the overall structure, we place tiny engineered structures inside the material itself. At that point, the distinction between a “material” and a “structure” begins to blur.
But must the behaviour remain fixed after manufacture? Not necessarily. In magneto-responsive metamaterials, flexible structures can contain tiny magnetic particles whose magnetisation is programmed in selected directions. Apply a magnetic field and these regions experience forces and torques, changing the geometry and therefore the mechanical response of the entire structure. This creates a remarkable possibility: the same metamaterial specimen can be programmed to behave as a soft, highly compliant material in one state and as an extremely stiff, metal-like material in another, with the change triggered remotely and on demand. It is almost as if the material can decide what kind of material it wants to be, in real time! Such behaviour could enable adaptive aircraft structures, vibration isolators that stiffen only when needed, soft robots that switch between flexible and rigid states, and devices that reshape themselves in response to their surroundings.
The ingredients behind all of this are surprisingly familiar. Solid mechanics tells us how each small beam stretches, bends or buckles. Structural analysis tells us how thousands of such elements interact. Design turns those responses into useful functions. The possibilities become even richer when mechanics interacts with the wider engineering domains (that you may already have some idea about), such as magnetism, waves and electricity. The programmable interactions with mechanics can lead to structures that move under magnetic fields, suppress unwanted vibrations, sense their environment or harvest electrical energy from motion.
For me, this journey began with enjoying mechanics during my bachelor’s studies at Shibpur. A master’s at IIT took me deeper into structural mechanics. During my PhD as a Zienkiewicz Scholar at Swansea, I began to see mechanics differently. The equations used to calculate deformation and stress were not only tools for predicting whether a structure would survive. They could become tools for inventing behaviours that conventional materials simply do not possess. That idea continued through my postdoctoral research at Oxford and later as an assistant professor at IIT Kanpur, opening possibilities ranging from vibration control and impact protection to adaptive structures, robotics and energy harvesting. Today, I lead the Programmable Matter Lab at the University of Southampton, where we design mechanical metamaterials and adaptive structures that can control vibration and impact, harvest energy, and tune their own mechanical response for demanding multi-functional applications across aerospace, civil, mechanical and marine engineering.
So the next time you calculate how a beam bends, consider this: that little beam could be the building block for a wonder material that does something nobody expected!
Interested in knowing more?
1. Sinha P., Mukhopadhyay T. (2023) Programmable multi-physical mechanics of mechanical metamaterials, Materials Science & Engineering R, 155 100745
2. Schaedler T. A., Carter W. B. (2016). Architected cellular materials. Annual Review of Materials Research, 46(1), 187-210.
Note: This is an invited article for the annual engineering and technology magazine of IIEST Shibpur
